Custom Pipes

Angular 2 allows you to create your own custom pipes:

import {Pipe, PipeTransform} from '@angular/core';

@Pipe({name: 'length'})
export class LengthPipe implements PipeTransform {
  transform(value:string, displayMessage: boolean): string {
    return displayMessage ? `${value} ${value.length}` : `${value.length}`
  }
}

Each custom pipe implementation must:

have the @Pipe decorator with pipe metadata that has a name property. This value will be used to call this pipe in template expressions. It must be a valid JavaScript identifier.
implement the PipeTransform interface's transform method. This method takes the value being piped and a variable number of arguments of any type and return a transformed ("piped") value.

Each colon-delimited parameter in the template maps to one method argument in the same order.

import {Component} from '@angular/core';
import {LengthPipe} from './length.pipe';

@Component({
	selector: 'Hello',
	template: '<div><p>{{ message | length:true }}</p><p>{{ message | length:false }}</p></div>',
	pipes: [LengthPipe]
})
export class Hello {
  message: string = 'Hello There';
}